vtop

vtop takes more of a graphical approach to top, while concentrating more on simplicity. It displays CPU and Memory usage live charts, as well as a running process list. It runs on Node.js and can be easily installed with npm install -g vtop.

gtop

gtop takes the graphical interface of vtop to another level. Just like vtop, it also displays a live chart of both CPU and memory, however gtop adds a network live chart to the list, and pie charts for both memory and swap, as well as storage usage.

gtop also runs on Node.js, and can easily be installed with npm install gtop -g.

s-tui

While s-tui is not a process monitoring utility, it displays great information about your process status. It's python based and uses little resource. You can easily install it with sudo pip install s-tui.